AT511414A1 - Doped HEXAGONAL TUNGSTEN CARBIDE AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Abstract

The present invention relates to a Wolframmonocarbidpulver based on a, with at least one transition metal of the 4th and / or 5th and / or 7th transition group, hexagonal Wolframmonocarbids whose fine or finest particles have a fine or finest crystallite structure. In this case, corresponding to the respective mole percent of the transition metal or the sum of the transition metals, tungsten atoms within the hexagonal crystal structure of Wolframmonocarbids replaced by atoms of / the transition metals used, thereby forming the doped hexagonal tungsten carbide. In particular, the invention relates to a very specific two-step process for the preparation of new doped hexagonal tungsten carbides via (W, Me) 2C to (W, Me) C. (Fig. 2)

Description

To begin with, the definitions of terms are to be given with respect to the specification and the claims:

Particles: Describes individual powder structures (particles), which can be monocrystalline or polycrystalline,

Crystallite: a distinction is made between monocrystalline particles (consisting of a crystal fit) and polycrystalline particles (consisting of 2 or more crystallites separated by grain boundaries, crystallite = grain, FIG. 1),

Agglomeration: Joining of fine particles by surface forces to larger powder structures.

Average Particle Size: Average diameter of the particles of a powder, assuming that all particles are spherical and of equal size. Powders can be analyzed in their as-delivered condition or after deagglomeration or milling. One method of measuring average particle size is the Fisher Subsieve Sizer.

Particle size distribution: For given values (size intervals) of a particle feature, the proportions are determined. From this one obtains a quantity distribution of the characteristic concerned.

Particle / crystallite growth: Describes on the one hand the increase of the mean particle size by growth processes, on the other hand the growth of the crystallites, which build up a particle.

For a more detailed explanation of the above terms, reference is made to FIG. 1.

The diagram there shows a crystallite 1, a monocrystalline particle 2, a polycrystalline particle 3a with crystallite boundary 3b and the agglomerate 4.

Description:

The present invention relates to a novel tungsten carbide, which can be prepared at high carburization temperatures within short reaction times and contrary to expectation even at high reaction temperatures to no or only to a very limited extent tends to a particle / crystallite size increase.

It is known that in chromium-doped tungsten carbide, the chromium acts as a particle and crystallite growth inhibitor in carburization at high temperatures. In addition, according to A. Kleiner: Hard material and metal powder with nanocrystalline amplification phases, Vienna University of Technology, Diss., 2006 to a grain fine

Effect come with carbide sintering. The particle- and crystallite-growth-inhibiting effect in carburization is based on the high solubility of chromium in the tungsten subcarbide, W2C and on the low solubility of Cr in the hexagonal tungsten monocarbide, WC: The dopant Cr is first dissolved in the subcarbide, but then diffuses into the further carburization Monocarbide again from the lattice, Thus, the chromium separates out at emerging crystallite boundaries, presumably as (Cr, W) 3C2 (= orthorhombic) or as {W, Cr) 2C (= hexagonal) and it produces carbide powders consisting of polycrystalline Particles exist (so-called "blackberries"). In the publication by A. Bock and B, lines Production and characterization of ultrafine toilet powders, Plansee Seminar, 2001, TEM and EDX proved that the chromium in the polycrystalline WC particles is preferentially present at the WCWVC crystallite boundaries.

In EP 808912 B2 (Allied Materials), the method for grain refining (formation of polycrystalline particles) is described in more detail. Here tungsten powder is mixed with a mean particle size of 1 to 7 pm with a chromium-containing powder and carbon black and then to 1200 to 1700 ° C heated. The average particle size of the starting tungsten powder plays a crucial role according to this document. If it exceeds 7 pm, the diffusion rate of chromium is insufficient to diffuse to the center of the particles. As a result, this leads to an inhomogeneous hard metal structure. On the other hand, if the particles are smaller than 1 pm, uneven diffusion of the chromium into the tungsten and during the heat treatment will result in sintering of the W particles and extraordinary growth.

Excessively high concentrations lead to the exceeding of the Cr solubility in the carbide, which leads to the formation of chromium-rich phases which reduce the strength.

In the work of Z. Tukör: Chromium doping of tungsten carbides, Vienna University of Technology, Diss., It was shown in 2009 that the particle size of the tungsten powder can also be below 1 pm and> 7 pm and not, as just described, between 1 and 7 pm must be in order to obtain a homogeneous hard metal structure. To prevent local particle and crystallite growth, it is important to introduce the chromium as evenly as possible before carburizing. A. Kleiner, supra, attempted this by incorporating chromium prior to reduction of the W03 powder to the W metal. For this, the oxide powder was impregnated with a solution containing chromium. A better distribution of chromium was achieved by A.M. Adorjan [18] by spray-drying a chromium-containing ammonium tungstate solution.

EP 1420076 A1 discloses a hard metal alloy which has 5 to 50% of a metallic binder phase with Co, Ni and Fe as the main component and 0 (zero) to 40% by volume of a cubic crystal compound which comprises at least one carbide and / or a nitride of a compound selected from metals of Groups IVB, VB, and VIB of the PSE, balance tungsten carbide (WC), wherein at least one element from the group Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, Mn and Re in the crystal of the hexagonal WC in solid solution in an amount of 0.1 to 3 wt .-%, each based on the amount of WC is present.

The doped with the various elements toilet powder should lead to carbide alloys, which are characterized by increased (n) hardness, toughness, heat resistance, corrosion and oxidation resistance.

The preparation of the doped WC powder used in the hard metal alloys is carried out according to this EP-A1 in a merely one-stage production process by carburizing compounds containing said metals.

It has been found that in a one-step process for producing tungsten carbide doped with transition-group metals, solid solution of the corresponding carbides in the hexagonal doped WC crystal can not be achieved without additional occurrence of interfering cubic phases of the transition metal carbides.

Thus, it is not possible to achieve the proportion of cubic transition metal carbides specified in claim 1 of EP-A1 with 0 (groove)% in addition to the hexagonal phase of the doped WC.

Starting from the known investigations and production processes of tungsten carbide doped with the transition metals in question and their result, it was attempted to be known from the only hitherto known doping elements from the 6th group of transition metals (Cr and Mo) - of whose mixed carbides that they are permanently soluble in the hexagonal WC - get away and go through doping with elements of the adjacent transition metal groups to tungsten carbide, which lead at high reaction temperatures and thus significantly shortened reaction times to doped WC powder, characterized by particularly small crystallite sizes and average particle sizes and characterized by particularly low particle / crystallite growth at high temperatures. The smaller crystallite sizes and smaller average particle sizes save in particular the high cost of grinding the extremely hard carbides, which is advantageous in view of the high wear of the grinding tools. Furthermore, the properties of the cemented carbide can be positively influenced by the control of the crystallite size, the average particle size and the particle size distribution of the carbide powder. This concerns, for example, new combinations of hardness and toughness. · «·· ·

It should therefore be prepared in a short time and without costly post tungsten carbide powder, which is suitable for the manufacture and equipment of various carbide tools by sintering, and wherein the case known unwanted particles / crystallite magnification is obstructed.

The invention relates to a new carbide powder with fine or finest crystallite and average particle size, based on a stoichiometric

Tungsten monocarbide (atomic ratio of W: C = 1: 1) which has been doped with a transition metal.

This carbide powder is characterized in that it consists of a tungsten monocarbide having a hexagonal crystal system which contains at least one metal of the 4th and / or 5th and / or 7th (except Tc) group of the transition metals or of the 18 groups -

Periodic system is doped4 - wherein - the respective mole percent of the transition metal or the sum of the transition metals accordingly - individual tungsten atoms within the hexagonal crystal lattice of the stoichiometric tungsten monocarbide replaced by atoms of at least one of the metals of the above transition metal groups.

It has been found that it is very important that the doping metal of the transition metal groups in question practically not, e.g. as cubic carbide next to the tungsten carbide having a hexagonal crystal structure, for example at the WC crystallite boundaries, but that it is actually incorporated into the hexagonal crystal structure of the WC in place of the tungsten atoms, ie in the doped hexagonal (W, Me) C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] is firmly dissolved.

In accordance with claim 2 it can be provided that the WC powder consists of at least one metal of the 4th and / or 5th and / or 7th (except Tc) group of transition metals and additionally chromium and / or molybdenum doped tungsten monocarbide [(W , Cr, Mo, Me) C, (W, Mo, Me) C, (W, Cr, Me) C, Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re].

The claim 3 it can be further seen that it is particularly advantageous if the forming the powder hexagonal doped tungsten carbide ^ (W, Me) C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re], to a total of 0.1 to 3 mol%, based in each case on WC, by adding (doping) of at least one of the mentioned in claim 1 or doped by the respective sum of the transition metals mentioned in claim 1.

Furthermore, it has proven to be advantageous, in particular with regard to the low crystallite and small average particle size, if, as provided according to claim 4, the tungsten carbide powder forming hexagonal doped tungsten carbide, (W, Cr, Mo, Me) 2C, (W, Mo, Me) 2C, (W, Cr, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta,

• · · ♦ *

Mn, Re], to a total of 0.1 to 3 mol%, in each case based on WC, by adding (doping) of at least one of the mentioned in claim 1 or with the respective sum of the transition metals mentioned in claim 1, in each case plus chromium and / or molybdenum is doped.

A further embodiment of the invention according to claim 5 provides that the new tungsten carbide powder can contain up to 1% by weight of cubic carbide phases of the elements of the fourth, fifth, sixth and seventh group of transition metals or Group Periodic Table contains.

Furthermore, the claim 6 provides that the lattice parameters a and c of the doped hexagonal tungsten carbide, in which the elements mentioned in claims 1 and 2 are dissolved, in the range

Lattice parameter a: 2.902 A to 2.911 A lattice parameter c: 2.830 A to 2.843 Å, especially in the range

Lattice parameters a: 2.903 A to 2.910 A lattice parameters c: 2.832 A to 2.840 Å.

Another very important object of the invention is the novel process for the preparation of transition-metal-doped tungsten carbide as described above.

For this purpose, the usual, ie conventional carburization of tungsten to tungsten carbide should be briefly discussed;

The same is done by admixing high purity carbon black and heating to 1300 ° C to 1700 ° C under a hydrogen atmosphere. This in turn leads to the intermediate formation of a precursor W2C, which is reacted in the presence of sufficient carbon equal to the toilet. It is therefore important to mix the carbon well with the tungsten in order to minimize the transport routes within the W as possible. The hydrogen atmosphere causes a concentration of the carbon over other areas, as small amounts of hydrocarbon arise, which are where there is little carbon, decomposed to carbon and hydrogen, such as Tungsten: Properties, Chemistry, Technology of the Element, Alloys and Chemical Compounds, Klüver Academic, 1999.

The mean particle size and particle size distribution of the tungsten powder used are ultimately determinative of the crystallite and average particle size of the tungsten carbide. The smaller the average particle size of tungsten, the lower carburization temperatures are necessary to obtain WCs of small crystallite size and small mean particle size. A. Bock, W.D. Schubert and B. Lux: Grain / Particle growth of ultrafine WC during W - Powder carburization, Vienna University of Technology, 1997 investigated the carburization of ultrafine tungsten powder in the range of 900 ° C to 1900 ° C. It was found that increasing the carburization temperature from 900 DC to 1500 ° C increased the mean particle size of e.g. 0.1 pm to 0.2 pm (BET). However, increasing the carburization temperatures from 1500 ° C to 1900 ° C resulted in significant particle growth of up to 3.5 pm.

Carburization of ultrafine tungsten metal powders (0.1 pm-0.5 pm) at lower temperatures (1200 to 1500 DC) therefore seems to be of advantage. However, other phenomena occur:

The WC crystallites have a high proportion of crystallographic defects that can provide high reactivity during sintering of the cemented carbide.

The reaction time to obtain stoichiometric WC increases from 1.5h at 1200 ° C to 7h at 900 ° C.

At low carburization temperatures, highly reactive carbon must be used (Flame soot: BET = 74 m2 / g) instead of standard carbon black (BET = 7-10 m2 / g).

The average particle size can be reduced by reducing the carburization temperature only to a limit corresponding to a calculated BET particle size of about 90 nm.

It was, as briefly stated above, now found that the above-mentioned disadvantages of low carburizing temperatures can be avoided if, for example, by adding Ti, V or Ta, while maintaining low crystallite size and low mean particle size of the WC, carburized at high temperatures , These additives, which are usually added as "grain growth inhibitors during sintering of a hard metal, also have an effect on the tungsten subcarbide during the carburization of the tungsten and thus do not have to be introduced in the next step. It is important that the additives be evenly distributed throughout the powder as it is believed that they affect the surface tension of the WC and / or slow down the crystallite boundary migration, reduce the annealing of the crystallite boundaries and prevent coalescence of the particles, thereby causing them to carburize effective particle / anti-crystallitic effect. · * · T * * * C * ·? * · I a ♦ Λ · * t ♦ * ♦ * • * * * · ί · · *

It has been found that a true solution of transition metals of the groups defined above in the hexagonal tungsten carbide (WC) without excretion of e.g. cubic phases of the doping metal carbides can be achieved by a two-stage process by specifically first a doped tungsten subcarbide, (W, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re], which then in The second step is carburized to the doped woiframmonocarbide (W, Me) C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re].

Accordingly, a very significant further object of the present invention according to claim 7 in a new method for producing a fine or very fine crystalline fine and having fine particles, doped with at least one transition metal, tungsten carbide powder, as described above in its variants.

The novel process for the production of finely crystalline doped Woiframmonocarbid (WC) with fine or fine particles is characterized in that - in a first stage - a mixture of tungsten metal powder with carbon black and / or graphite and the Powder of at least one compound, in particular an oxide of the above transition metals for 1 to 20 hours, especially 2 to 5 hours, ground and / or mixed and at temperatures in the range of 1300 to 1900 ° C, preferably 1450 to 1700 ° C, in Presence of an excess of hydrogen, preferably in the hydrogen stream, to carburize to the sub-carbide doped with the respective transition metal (s) (W.Me.sub.C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] in that - in an intermediate stage - the resulting doped tungsten subcarbide (W, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] is broken and / or deagglomerated, and in a second stage - the resulting powder of the doped tungsten subcarbide (W, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] with carbon black and / or graphite, preferably in an amount stoichiometrically necessary for the preparation of the doped woiframmonocarbide (atomic ratio (W + Me): C = 1: 1, with Me = at least one of the metals of the above-mentioned transition metal groups) - 1 to 20 hours, in particular 2 to 5 hours milled and / or mixed and in the presence of an excess of hydrogen, preferably in Hydrogen stream at, preferably, a temperature within a range between 1400 and 2300 ° C, in particular from 1500 to 1950 ° C, to which with the respective transition metal (s) doped Woiframmonocarbid (W, Me) C [Me = Ti , Zr, Hf, V, Nb, Ta, Mn, Re] - after which the doped woiframmonocarbide (W, Me) thus obtained C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] broken and / or ground and / or sieved. • • • * * pj * · · · «« © «·· -« * | * * · · · «« * ·· · tti * * · • · • *

Another object of the invention is a doping with chromium and / or Mo in addition to at least one of the claimed transition metals of the 4th, 5th and 7th group of the PSE, being provided according to claim 8, - that - in a first stage - a mixture of tungsten metal powder with carbon black and / or graphite and the powder mixture of a compound, in particular an oxide of chromium and / or molybdenum, with at least one compound, in particular an oxide of one of the transition metals 1 to 20 mentioned in claim 1, in particular 2 in the presence of an excess of hydrogen, preferably in the hydrogen stream, to which with the mixture of. to 5 h, long milled and / or mixed and at, preferably a temperature in the range of 1300 to 1900 ° C., especially at 1450 to 1700 ° C. Chromium and / or molybdenum and the at least one transition metal doped tungsten subcarbide (W, Cr, Mo, Me) 2C, (W, Mo, Me) 2C, (W, Cr, Me) 2C [Me = Ti, Zr, Hf, V , Nb, Ta, Mn, Re] karbur - that - in an intermediate stage - the thus-obtained doped tungsten subcarbide {W, Cr, Mo, Me) 2C, (W, Mo, Me) 2C, (W, Cr, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] is broken and / or deagglomerated, and that - in a second stage - the resulting powder of the doped tungsten subcarbide (W, Cr, Mo, Me) 2C, (W, Mo, Me) 2C, (W, Cr, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] with carbon black and / or graphite - preferably in a stoichiometric manner for the preparation of the doped tungsten monocarbide required amount {atomic ratio (W + Me): C = 1: 1, with Me = at least one of the metals of the above-mentioned transition metal groups) - 1 to 20, in particular 2 to 5 hours, long and / or mixed and in the presence of an excess at hydrogen, preferably in the hydrogen stream, at, preferably a temperature within a range between 1400 and 2300 ° C, in particular from 1500 to 1950 ° C, to the stoichiometric W doped with the respective transition metal (s) carbamate (W, Cr, Mo, Me) C, (W, Mo, Me) C, (W, Cr, Me) C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] - after which the thus-obtained doped tungsten monocarbide (W, Cr, Mo, Me) C, (W, Mo, Me) C, (W, Cr, Me) C [Me = Ti, Zr, Hf, V, Nb, Ta , Mn, Re] broken and / or ground and / or screened.

It is advantageous if, as claimed in claim 9, it is ensured that the tungsten metal powder having an average particle size in the range between 0.5 and 10 μm (FSSS as supplied), preferably from 0.50 to 1.0 gm ( FSSS as delivered).

In an analogous manner, it is advantageous if the carbon black and / or the graphite having a mean particle size of less than 1 pm (FSSS as supplied) is used. • * * * *

Last but not least, it has proved to be advantageous if the compound (s), in particular the oxide (s) of the transition metal (s) provided for doping with an average particle size of less than 1 μm (FSSS in the as-delivered state) is used (become).

Examples:

The following examples illustrate the invention in more detail:

Example 1: This example demonstrates the properties of undoped tungsten carbide (WC) produced at three different temperatures from tungsten subcarbide (W2C). a) Preparation of tungsten subcarbide (W 2 C): 9683.7 g of tungsten metal powder having an average particle size of 0.66 μm (FSSS as received) was mixed with 316.3 g of carbon black having a mean particle size of < 1 pm in a grinding drum with

Grinding balls mixed for 2 to 5 hours to obtain the subcarbide (W2C) by carburizing at 1630 eC in a hydrogen stream.

The product thus prepared was crushed and deagglomerated in a ball mill. b) Preparation of tungsten carbide (WC) from tungsten subcarbide (W 2 C): Next, the powder was added with the amount of carbon black needed to produce stoichiometric hexagonal tungsten carbide (WC) in another carburization step.

After the addition, mixing was carried out for 2 to 5 hours in a ball mill, and the carburization was carried out at three different temperatures (1450 ° C, 1630 ° C, 1950 ° C). The results are shown in the following table.

Carburization lattice parameter [A] '----------- 1 temperature ac particle size (FSSS deagglomerated) [Mm] total carbon material [%] 1450eC 2.906961 (+48) 2.838334 (± 66) 1.32 6, 26 1630 ° C 2.907419 (+54) 2.838513 (+72) 1.81 6.18 1950 ° C 2.907007 (± 60) 2.838258 (± 72) 3.43 6.14

Although the results show virtually little change with respect to the lattice parameters a and c, further a slight decrease in the Gesamtkohtenstoffgehaits, but a substantial increase in the average particle size (FSSS deagglomerated) by about 2.5 times within a carburization temperature range between 1450 and 1950 ° C, the mean particle size is already at the low

Carburization temperature of 1450 ° C is relatively high, so at 1.32 gm (FSSS deagglomerated) is. At 1950 cC, the particles are already sintered together and form solid agglomerates consisting of crystallites with a size of about 3 to 5 gm (see Fig. 2a).

The following examples show the properties or property changes of tungsten carbide (WC) doped with a metal from the 4th, 5th and 7th transition metal group:

Example 2:

Doping of WC with a Group 4 Transition Metal a) Preparation of Titanium-doped W 2 C:

Tungsten metal powder with an average particle size of 0.66 pm (as-received FSSS) was blended with carbon black having a mean particle size of < 1 pm and titanium dioxide (TiO 2) having an average particle size of < Mixed 1 pm.

In this case, 362.1 g of TiO 2 were mixed with 9599.4 g of W (metal powder) and 362.1 g of C (soot) for 2 to 5 hours in a grinding drum with grinding balls.

This was followed by carburization to the doped tungsten subcarbide (W, Ti) 2C at 1630 ° C in a stream of hydrogen. The resulting product was crushed and deagglomerated in a ball mill.

b) Preparation of titanium-doped WC

The (W, Ti) 2C powder prepared according to a) was then subsequently mixed with carbon black so that during a further carburizing step a stoichiometric hexagonal doped tungsten carbide (W, Ti) C is formed in which titanium is dissolved.

The powder mixture was again homogenized in a grinding drum with grinding balls for 2 to 5 hours and carried out the carburization at 1450 ° C in a stream of hydrogen. After breaking, milling and sieving the product, the lattice parameters are as follows;

a: 2.907149 (± 99) A

c: 2.838.490 (± 132) A

The mean particle size (FSSS deagglomerated) is 0.95 pm, the total carbon content at 6.32 w%.

When carburizing to hexagonal WC is performed at 1630 ° C, the lattice parameters are as follows:

a; 2.907434 (± 75) A

c: 2.838461 (± 96) A

The average particle size (FSSS deagglomerated) is 1.07 μιτι, the total carbon content at 6.30 w%.

When carburizing to hexagonal WC at 1950 ° C, the lattice parameters are:

a: 2.907127 (± 48) A

c: 2,837,986 (± 66) A

The mean particle size (FSSS deagglomerated) is 1.34 pm, the total carbon content is 6.28 w%.

The results show essentially constant carbon content, and at substantially constant lattice parameters a and c, starting from a compared to undoped WC by more than a quarter lower average particle size of the Ti-doped WC at a carburization temperature of 1450 ° C only a slight increase in the Particle size only about one-third in the temperature range of 1450 ° C to 1950 ° C. Even at 1950 ° C, the very fine, individually present particles are still fine polycrystalline, the crystallite size is less than 1 pm (see Fig. 2b).

Example 3:

Doping WC with a Group 5 Transition Metal: a) Preparation of Tantalum-doped W2C:

Tungsten metal powder with a mean particle size of 0.66 pm (as-received FSSS) was mixed with carbon black having a mean particle size of < 1 pm and tantalum oxide (Ta 2 O 5) having an average particle size of < Mixed 1 pm.

In this case, 662.85 g Ta205 were intimately mixed with 17.832.5 g W (metal powder) and 690 g C (soot) for 2 to 5 hours in a grinding drum with grinding balls.

Thereafter, the carburization was carried out to tungsten subcarbide (W, Ta) 2C at 1630 ° C in a stream of hydrogen. The product was broken and deagglomerated in a ball mill. b) Preparation of tantalum doped WC:

The (W, Ta) 2C powder prepared according to a) was then subsequently mixed with carbon black so that during a further carburizing step a stoichiometric hexagonal doped tungsten carbide (W, Ta) C is formed in which tantalum is dissolved. The powder mixture was again homogenized in a grinding drum with grinding balls for 2 to 5 hours and carried out the carburization at 1450 ° C in a stream of hydrogen. After breaking, milling and sieving the product, the lattice parameters are:

a; 2.908764 (± 75) A c: 2.839832 (± 96) A

The average particle size (FSSS deagglomerated) is 1.17 μηι, the

Total carbon content at 6.15 w%.

When carburizing to the hexagonal WC at 1630 eC, the lattice parameters are as follows: a: 2.908826 (± 60) c: 2.839195 (± 81) A

The average particle size (FSSS deagglomerated) is 1.25 μπι, the

Total carbon content at 6.18 w%.

When carburizing to hexagonal WC at 1950 ° C, the lattice parameters are as follows: a: 2.910473 (± 63) λ c: 2.840489 (± 87) Å

The average Teiichengröße (FSSS deagglomerated) is 1.7 μηι, the

Total carbon content at 6.22% w.

At substantially constant carbon contents, the average particle size of the Ta-doped WC at a carburization temperature of 1450 ° C below that of undoped WC and increases by about half up to a temperature of 1950 ° C here, too. The particles are very finely and finely polycrystalline at 1950 ° C. (crystallite size <1 μm). The lattice parameters a and c are shifted to higher values than the undoped WC powder,

Example 4: a) Preparation of vanadium doped W 2 C:

Tungsten metal powder with a mean particle size of 0.66 pm (as-received FSSS) was mixed with carbon black having a mean particle size of &lt; 1 pm and vanadium pentoxide (V2C> 5) having an average particle size of &lt; Mixed 1 pm.

In this case, 146.8 g of V205 were thoroughly mixed with 9594.7 g of W (metal powder) and 371.6 g of C (soot) for 2 to 5 hours in a grinding drum with grinding balls.

Thereafter, the carburization to tungsten subcarbide (W, V) 2C was carried out at 1630 ° C in a hydrogen stream. The product was broken and deagglomerated in a ball mill. b) Preparation of vanadium-doped WC:

The (W, V) 2C powder prepared according to a) was subsequently mixed with carbon black so that during a further carburizing step a stoichiometric hexagonal doped tungsten carbide (W, V) C is formed in which vanadium is dissolved. The powder mixture was again in a grinding drum with

Homogenization of grinding balls for 2 to 5 hours and carried out the carburization at 1450 ° C in a stream of hydrogen.

After breaking, milling and sieving the product, the lattice parameters are:

a: 2.904736 (± 90) A

c: 2,835,908 (+117) A

The mean particle size (FSSS deagglomerated) is 1.18 pm, the

Total carbon content at 6.27% w.

When carburizing to hexagonal WC is performed at 1630 ° C, the lattice parameters are as follows:

a: 2,905,341 (+66) A c: 2,835,610 (+87) A

The mean particle size (FSSS deagglomerated) is 1.18 pm, the

Total carbon content at 6.30 w%.

When the carburization to the hexagonal WC is performed at 1950 ° C, the lattice parameters are as follows: a: 2,905,896 (+42) Å

c: 2,835,866 (± 57) A

The mean particle size (FSSS deagglomerated) is 1.48 pm, the

Total carbon content at 6.29 w%.

Also, this example shows substantially consistent carbon levels at carburization temperatures of 1450 ° C to 1950 ° C and the mean particle size is 1450 ° C below that of undoped WC and rises to 1950 ° C by only about a quarter. Even the powders produced at a carburization temperature of 1950 ° C consist of very fine, polycrystalline particles. The crystallite size is less than 1 pm (see FIG. 2c). The lattice parameters a and c are opposite to the undoped ones

Tungsten carbide powder shortened.

Example 5: a) Preparation of Rhenium-doped W2C:

Tungsten metal powder with an average particle size of 0.66 pm (FSSS as received) was mixed with graphite having an average particle size of 1-5 μm and rhenium powder (Re).

In this case, (1.5% Re) 147.1 g Re with 9536.6 g of W {metal powder) and 316.3 g of C (synthetic graphite) were intimately mixed for 2 to 5 hours in a grinding drum with grinding balls.

This was followed by carburization to tungsten subcarbide (W2C) at 1630 ° C in a stream of hydrogen. The product was broken and deagglomerated in a ball mill. b) Preparation of rhenium doped WC:

The (W, Re) 2C powder prepared according to a) was then subsequently mixed with carbon black so that during a further carburizing step a stoichiometric hexagonal doped tungsten carbide (W, Re) C is formed, in which rhenium is dissolved. The powder mixture was again homogenized in a milling drum with grinding balls for 2 to 5 hours and the carburization was carried out at 1450 ° C in a hydrogen stream, a: 2.906920 (+52) Å

c: 2.838321 (± 74) A

The mean particle size (FSSS deagglomerated) is 1.27 pm, the

Total carbon content at 6.17% w.

When carburizing to hexagonal WC is performed at 1630 ° C, the lattice parameters are as follows:

a: 2,907399 (± 39) A

c: 2.838480 (± 68) A

The mean particle size (FSSS deagglomerated) is 1.74 pm, the

Total carbon content at 6.14 w%.

When carburizing to hexagonal WC at 1950 ° C, the lattice parameters are:

a: 2.906933 (± 48) A

c: 2.838225 (± 76) A

The mean particle size (FSSS deagglomerated) is 3.15 pm, the

Total carbon content at 6.18 w%.

The following example shows the results of the preparation of vanadium (5th group) and chromium (6th group) doped WCs:

Example 6: a) Preparation of Vandanium plus chromium doped W2C:

Tungsten metal powder with a mean particle size of 0.66 pm (as-received FSSS) was mixed with carbon black having a mean particle size of &lt; 1 pm, vanadium pentoxide (V2Os) and chromium oxide (Cr 2 O 3) having an average particle size of &lt; Mixed 1 pm.

For this purpose, 73.4 g of V205 and 61.3 g of Cr 2 O 3 were mixed with 9593.8 g of W (metal powder) and 361.9 g of C (soot) for 2 to 5 hours in a grinding drum with grinding balls.

Thereafter, the carburization to tungsten subcarbide (W, Cr, V) 2C) was carried out at 1630 ° C in a stream of hydrogen. The product was broken and deagglomerated in a ball mill. b) Preparation of vanadium plus chromium doped WC:

The (W, Cr, V) 2C powder prepared according to a) was then subsequently mixed with carbon black so that during a further carburizing step a stoichiometric hexagonal doped tungsten carbide (W, Cr, V) C is formed, in which vanadium and chromium are dissolved , The powder mixture was again homogenized in a grinding drum with grinding balls for 2 to 5 hours and carried out the carburization at 1450 ° C in a stream of hydrogen. After crushing, grinding and sieving the product, the lattice parameters are as follows: a: 2.903943 (± 87) A

c: 2,835,421 (± 117) A

The mean particle size (FSSS deagglomerated) is 1.31 μπη, the

Total carbon content at 6.27% w.

When carburizing to hexagonal WC is performed at 1630 ° C, the lattice parameters are as follows:

a: 2.904820 (+63) A

c: 2,835,190 (± 81) A

The mean particle size (FSSS deagglomerated) is 1.33 pm, the

Total carbon content at 6.26% w.

If the carburization is performed to the hexagonal WC at 1950 ° C, the lattice parameters are as follows:

a: 2,905,563 (± 57) A

c: 2,835,787 (± 81) A

The mean particle size (FSSS deagglomerated) is 1.47 pm, the

Total carbon content at 6.32 w%.

In this tungsten carbide doped with one metal each of the 5th and 6th transition metal group, with substantially constant carbon content, this mixed-doped WC had a small mean particle size at the carburization temperature of 1450 ° C., which barely increased up to 1950 ° C. , and is very low with the value of less than 1.5 pm. These small particles again consist of crystallites whose size is less than 1 pm. The lattice parameters a and c of the tungsten carbide powder produced at 1950 ° C. are shortened compared with the undoped powder.

In general, it can be said that with increasing temperature to ever increasing differences between the undoped and the doped powder. While sintered agglomerates consisting of large crystallites form in the undoped powder, only a slight loose (!) Agglomeration is observed with doped powders even at high temperatures, and the fine particles constituting the powder consist of very fine crystallites.

The invention will be explained in more detail with reference to FIGS. 2a to 2c:

They show copper micrographs (Scanning Electron Microscope - backscattered electrons (BSE)) of the monocarbides carburized at 1950 ° C to show the reduced particle and crystal growth through the doping, namely a) undoped, b) Ti-doped and c) V-doped.

Claims (11)

Claims 1. A carbide powder consisting of fine particles based on one or more transition metals doped stoichiometric tungsten carbide (atomic ratio of W: C = 1: 1, tungsten monocarbide, WC) whose particles have a fine or very fine crystallite structure which is characterized in that it consists of a tungsten monocarbide having a hexagonal crystal system, which metal oxide is at least one metal of the 4th and / or 5th and / or 7th, excluding Tc group of the transition metals or the 18-group Periodic system is doped, - - wherein - the respective mole percent of the transition metal or the sum of the transition metals accordingly - individual tungsten atoms within the hexagonal crystal lattice of the stoichiometric tungsten monocarbide are replaced by atoms of at least one of the metals of the above transition metal groups. 2. tungsten carbide powder according to claim 1, characterized in that it consists of at least one metal of the 4th and / or 5th and / or 7th (except Tc) group of transition metals and additionally chromium and / or molybdenum doped hexagonal Wolframmonocarbid [(W, Cr, Mo, Me) C, (W, Mo, Me) C, (W, Cr, Me) C, Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Rej. 3. Tungsten carbide powder according to claim 1, characterized in that it forms the hexagonal doped tungsten monocarbide, (W, Me) C (Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re), to a total of 0, 1 to 3 mol%, in each case based on WC doped with one of or with the respective sum of the transition metals mentioned therein. 4. Tungsten carbide powder according to claim 2, characterized in that it is formed hexagonal doped tungsten carbide, (W, Cr, Mo, Me) 2C, (W, Mo, Me) 2C, (W, Cr, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn. Re], to a total of 0.1 to 3 mol%, in each case based on WC, with at least one of the mentioned in claim 1 or with the respective sum of the transition metals mentioned in claim 1, each plus chromium and / or molybdenum doped. 5. tungsten carbide powder according to one of claims 1 to 4, characterized in that it contains up to 1% by weight of cubic carbide phases of the elements of the mentioned in claim 1 4, 5 ,, 6, and 7, group of transition metals or of the 18th Group periodic table contains 6, tungsten carbide powder according to one of claims 1 to 5, characterized in that the lattice parameters a and c of the doped hexagonal tungsten carbide, in which the elements mentioned in claims 1 and 2 are dissolved, in the range lattice parameters a: 2.902 Ä to 2.911 Lattice parameters c: 2.830 A to 2.843 Å, especially in the range of lattice parameters a: 2.903 A to 2.910 A lattice parameters c: 2.832 Å to 2.840 Å. 7, A method for producing a fine or ultrafine particles, at least one transition metal doped tungsten carbide powder whose particles have a fine or finest crystallite structure, according to claim 1 or 3, characterized in that - in a first stage - a mixture of tungsten metal powder with carbon black and / or graphite and the powder of at least one compound, in particular an oxide of the transition metals mentioned in claim 1 for 1 to 20 hours, especially 2 to 5 hours, ground and / or mixed and at temperatures in the range of 1300 to 1900 ° C, preferably 1450 to 1700 ° C, in the presence of an excess of hydrogen, preferably in the hydrogen stream, to the tungsten subcarbide doped with the respective transition metal (s) (W, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] is carburized, that - in an intermediate stage - the thus obtained doped tungsten subcarbide (W, Me) 2C [Me = Ti, Zr, Hf, V , Nb, Ta, Mn, Re] are broken and / or deagglomerated, and that - in a second stage - the resulting powder of the doped tungsten subcarbide (W, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] with carbon black and / or graphite preferably in a stoichiometrically necessary for the preparation of the doped tungsten monocarbide amount (atomic ratio (W + Me): C = 1: 1, with Me = at least one of the above metals 1 to 20 hours, in particular 2 to 5 hours and / or mixed and in the presence of an excess of hydrogen, preferably in the hydrogen stream, at, preferably, a temperature within a range of 1400 to 2300 ° C, in particular of 1500 to 1950 ° C, to which tungsten monocarbide doped with the respective transition metal (s) (W, Me) C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] is carburized, - after which the thus-obtained doped tungsten monocarbide (W, Me) C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re ] is broken and / or ground and / or sieved. 8. A process for the preparation of a fine or, very fine particles, with a mixture of chromium and / or molybdenum and at least one of the transition metals mentioned in claim 1 doped tungsten carbide powder whose particles have a fine or finest crystallite structure, according to claim 2 or 4, characterized in that - in a first stage - a mixture of tungsten metal powder with carbon black and / or graphite and the powder mixture of a compound, in particular an oxide of chromium and / or molybdenum with at least one compound, in particular one Oxide of one of the above-mentioned transition metals 1 to 20, in particular 2 to 5 h, long and / or mixed and at, preferably a temperature in the range of 1300 to 1900 eC, in particular at 1450 to 1700 ° C, in the presence of an excess at hydrogen, preferably in the hydrogen stream, to which with the mixture of chromium and / or molybdenum and the at least one Transition metal-doped woiframine subcarbide (W, Cr, Mo, Me) 2C, (W, Cr, Me) 2C, (W, Mo, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] is carburized, that - in an intermediate stage - the thus obtained doped Woiframsubcarbid (W, Cr.Mo, Me) 2C, (W, Cr, Me) 2C, (W, Mo, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] are broken and / or deagglomerated, and that - in a second stage - the powder of the doped tungsten subcarbide (W, Cr, Mo, Me) 2C, (W, Cr, Me) 2C, (W, Mo, Me) 2C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] with carbon black and / or graphite - preferably in a stoichiometric manner for the preparation of the doped tungsten monocarbide required amount (atomic ratio (W + Me): C = 1: 1, with Me = at least one of the metals of the above-mentioned transition metal groups plus chromium and / or molybdenum) - 1 to 20, especially 2 to 5 hours, long and / or ground mixed and in the presence of an excess of hydrogen, preferably in a hydrogen stream, at, preferably one, temperature within of a range from 1400 to 2300 ° C, in particular from 1500 to 1950 ° C, to the stoichiometric tungsten monocarbide (W, Cr, Mo, Me) C, doped with the respective * * * * i Φ transition metal (s) W, Cr, Me) C, (W, Mo, Me) C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] is carburized, - after which the doped tungsten monocarbide (W, Cr, Mo, Me) C, (W, Cr, Me) C, (W, Mo, Me) C [Me = Ti, Zr, Hf, V, Nb, Ta, Mn, Re] broken and / or ground and / or is screened. 9. The method according to claim 5 or 6, characterized in that the tungsten metal powder having an average particle size in the range between 0.5 and 10.0 pm (FSSS in the delivery state), preferably from 0.50 to 1.00 pm (FSSS as delivered), 10. The method according to any one of claims 5 to 9, characterized in that the carbon black and / or the graphite having an average particle size of less than 10 pm (FSSS), preferably less than 1pm (FSSS), is used. 11. The method according to any one of claims 5 to 10, characterized in that the compound (s), in particular the oxide (s) of the (s) provided for doping transition metals (s) having an average particle size of less than 1 pm (FSSS ) is (are) used. Vienna, April 26, 2011